Metal boats are usually constructed by a process of forming metal sheets, for example two sheets side by side for the underwater panels, two side panel sheets joined at their front ends to a stem and along their lower edges to the underwater panels, and a sheet for the transom. The sheets are welded, where they join one another, frequently to extrusions of metal, and this welding operation is one of the most expensive operations in the construction of a boat hull. The most commonly used metal in such construction is marine grade aluminium, and this suffers with the phenomenon of a heat affected zone near the weld zone which is subject to cracking under fatigue loading. The invention herein is directed to improvements whereby the welding can be reduced or eliminated, and although the invention can, with the necessary changes, be applied to a boat having sheets of steel, it is described hereunder with reference to a boat having aluminium sheets.
In the U.S. Pat. No. 3,190,409 (Petterson) there was described a construction using a wedge shaped band forced between a plate and a leg of a slot, but this arrangement did not provide a positive interlock between the plate and joining strip, and experimental work by the inventor herein has established that an interlock is very desirable.
In the U.S. Pat. No. 3,190,408 of Petterson, there were further structures described and these included structures wherein sheets were joined by deforming an edge of each sheet to have an outstanding projection which entered into a slot of a joining strip and moved across in that slot to engage behind an abutment existing in the wall of the slot, and a key inserted to maintain engagement.
Experimental work conducted by the applicant herein has indicated that excellent results can be achieved with such construction. However the safety requirements for boats is such that a higher degree of integrity must be achieved and it is a main object of this invention to provide still further improvements.
It will be appreciated that with any vessel, particularly with a boat, the most vulnerable point of a hull is the corner between adjacent panels inclined at an angle to one another since such a point is the most likely point to encounter impact, and furthermore impact imparted to one panel can be transmitted to other panels through that point.
There are several situations which are frequently encountered in practice.
Firstly, if a sheet of metal forming a panel of a boat is subjected to impact between its ends, there will be a sliding of the sheet edge within its joining strip which will cause shearing of sealant between the surfaces and allow the boat to leak. The large mechanical advantage which exists to cause such sliding can cause movement of the end of the sheet away from the end of its joining strip, and it has been found desirable to provide means which will inhibit such sliding motion as much as possible.
If the corner between joining strips is subjected to impact, the resulting deformation of the channel walls is usually a spreading apart of those walls at that locality, and this also has the effect of separating the contiguous surfaces with the failure of the sealant therebetween. Once the joint fails at its end, progressive failure along the length of the joint could occur quite easily and this of course constitutes a serious hazard for leaking of water into the boat.